Carbohydrate type in PWO shakes

Post workout shakes should contain simple sugars to raise blood insulin right?

Perhaps not.

Simple sugars slow gastic emptying because they are highly osmotically activite. Maltodextrins in contrast, reach the small intestine, and hence are absorbed, more quickly.

The same can be said for the degree of protein hydrolysis - too much and it compromises gastric emptying…

I see a growing trend of more and more people moving towards slightly lower GI Carbs also PWO

How significant…what is the time difference in minutes (or seconds) between dextrose and other sugars? Are we talking about 10 x better or just a tad? What about GI issues with possible flora exchange? Any links to pubmed or is this just a concept? And what about glycemic differences? What scores do you have?

Actually, you should have both dextrose and maltodextrin. Either one by itself isn’t as effective as the combination.

Our goal post workout is to maintain a prompt digestion rate so nutrients can transport swiftly and efficiently to our muscles. With that said, it has been shown that this process slows when the ingested fluid contains a high osmolarity concentration (the second concept as shown below). Osmolarity is dependent on the number of particles in a solution. That is, a 100-milliliter solution with 20 glucose molecules will have a higher osmolarity then a 100-millileter solution that only contains 10 molecules. The shorter chain length a carbohydrate has, the higher it raises the solution’s osmolarity. Therefore, it is no surprise that a pure glucose solution (or dextrose, a monosaccharide) induces very high concentrations of solute (1, 3,4).

Fortunately these negative effects become greatly reduced when the drink contains a glucose polymer stacked with dextrose. But we still want a carbohydrate that is easily digested, and has a high Gl. Hence we use a combination of dextrose and maltodextrin. Osmolarity will be decreased, and glucose will still enter the blood stream at a proficient rate, thus maintaining its anabolic nature (1, 3).

A second factor concerning osmolarity must now be examined. From a clinical standpoint it is vital to take into consideration the fact that plasma (the liquid portion of blood) has an Osmolarity of 300 mOsm. This means that if one were to inject a solution with a greater concentration of solute into their blood, it would cause water from inside their red blood cells to leave by Osmosis (water always travels down its concentration gradient) and move into the plasma, in turn shrinking the erythrocytes (red blood cells). This is because the cells are iso-osmotic to the plasma (both have the same concentration of solute) (5).

A similar concept can be applied to your post workout meal. If a competitor were to consume a solution that was hypertonic or had a higher concentration of solute then 300 mOsm it could dehydrate them (showing why digestion is rightfully slowed in a high concentrated solution). The addition of maltodextrin once again solves this problem (2, 7).

The next question is, why not just use maltodextrin, and eliminate dextrose since it is so proficient? Shi. X et al. in an outstanding study tested the digestive effects of two substrates (any substance acted upon by an enzyme) as opposed to only one substrate in the small intestine. What they found was quite fascinating. The solution containing two substrates stimulated the activation of more transport mechanisms in the intestinal lumen, then did its singular counterpart. Therefore more carbohydrates were transported out of the small intestine (absorbed into the blood), which additionally aided a greater absorption rate of water into the blood stream (by osmosis). Thus, the higher activation rate of transport mechanisms, even with higher osmolarity facilitated faster energy uptake and hydration (6)!

  1. Beckers, E.J., et al.: Comparison of aspiration and scientific graphic
    Techniques for the measurement of gastric emptying rates in man
    Gut, 33:115,1992.

  2. Brouns, F., and Beckers, E.: Is the gut an athletic organ? Sports.
    Med., 15:242, 1993.

  3. Duchman, S.M., et al. Upper limit for intestinal absorption of a dilute glucose solution in men at rest. Med. Sci. Sports Exercise 29:
    482,1997.

  4. Schedl, H.P., et al. Intestinal absorption during rest and exercise:
    implications for formulating an oral re-hydration solution (ORS).
    Med. Sci. Sports Exerc., 26:267, 1994.

  5. Seiple, R.S., et al.: Gastric-emptying characteristics of two glucose
    polymer-electrolyte solutions. Med. Sci. Sports Exerc., 15:366,

  6. Shi, X., et al.: Effects of carbohydrate type and concentration and
    solution osmolality on water absorption. Med.Sci. Sports Exerc.,
    27:1607.1995.

  7. Vist, G.E., and Maughan, R.J.: Gastric emptying of ingested solutions in man: effect of beverage glucose concentration. Med. Sci.
    Sports Exerc., 26:1269, 1994.

I too can get into transfusion rates but what doest that equate into myofibril reconstruction…nice to have references but let’s get into simple math instead of flexing research available to everyone…when you use the Duchman study with subjects that are not involved with intense training we are getting a bit cloudy.

I’m sorry. I didn’t see the question on myofibril reconstruction until just now. :confused: Though really post-workout insulin does not actually build muscle - the purpsoe of post-workout carbohyrates is anti-catabolic (Journal of Applied Physiology; 82, 1882-1888, 1997.). The faster the carbohydrates you consume enter the bloodstream as glucose, the faster you can halt protein breakdown, increase blood vessel dilation and prepare for your second PW feeding which should contain mostly protein.

I was putting forth some evidence/theory in relation to the initial question asked regarding simple sugars, maltodextrin and gastric emptying and osmality.

And the Duchman study is completely relevent in the context used regardless of wether the subjects were at rest or not.

stellar points…we are about 4 years away from better research on how muscle improves from postworkout. Surge is a great formula on paper but I wonder if PW0 should be in three servings timed a bit differently…so may gaps.

How effective is Amylase? What limits does it have?

Then why whey and what does protein do? Pepsin from the stomach breaks down the amino acids into polypeptides and things get weird…

I agree - as of right now there is nothing concrete and what exactly a post workout shake should contain with regards to how much fluid volume, carb types and timing of carbs, protein and other nutrients (vitamins). I like much of John Berardi’s work on PW nutrition. I’ve never used Surge though…

I’m not sure if amylase supplementation will result in any noticable effects. I’ve used enzymes before in combination with protein and carbs and never really noticed any differences in recovery or intestinal function. I know of a few people who use it to help with abscesses though.

Surge does have some good points in terms of carbohydrate blend…but I was thinking of our natural Amylase…